Value of chemical mixture in multiple supralethal X-irradiation of mice

A chemical mixture containing 25 Amoles of MEA, 7 pmoles of AET, and 2 micromoles of 5-HT was found to be of significant value in protecting mice against repeated exposures of 800 R, 1100 R, or 1400 R given at intervals of 28 days. Dose-reduction factors of 2.17, 2.18, 1.95, 2.14, and 1.58 were obtained for the first five exposures. Following the first exposure there was no chemical mortality. The beneficial value of this mixture, however, was limited by the incidence of chemical toxicity which was more prevalent in mice with higher cumulative doses of radiation.     

Release of proteinase from mycelium of Mucor hiemalis

When Mucor hiemalis NRRL 3103 was grown in soybean medium, only a small fraction of the proteinase produced by the organism appeared in the culture filtrate, whereas the bulk of the enzyme was bound to the mycelial surface. Optimal pH of the proteinase ranged from 3.0 to 3.5. Inclusion of sodium chloride or other ionizable salts in the growth medium, however, resulted in the liberation from the mycelium of the loosely bound enzyme as it was formed. Maximal release of proteinase was achieved at a sodium chloride concentration of 0.5 m. The loosely bound proteinase was eluted also from intact resting mycelium by ionizable salts but not by water or by nonionizable substances. The amount of enzyme eluted from the mycelium depended upon the concentration of sodium chloride up to 0.3 m. Since liberation took place rapidly even at 0 C, a loose ionic linkage must exist rather than a biochemical binding of the enzyme to the mycelium. The recovery of proteolytic activity from repeated salt extractions was greater than that originally detected in the intact mycelium, possibly owing to unmasking of more active enzymes or functional groups. Further proteinase activity was released when salt-extracted mycelium was ruptured. Part of the proteinase thus observed was firmly attached to the cell fraction, and part of it appeared in the supernatant fluid. These conditions implied the presence of intracellular or firmly attached proteinase which could be partially released.     

Noncomplementarity in base sequences between the cohesive ends of coliphages 186 and lambda and the formation of interlocked rings between the two DNA's

The half molecules of 186 DNA have been isolated by the Hg(II)–Cs₂SO₄ density gradient centrifugal ion technique. The buoyant densities of the two halves in CsCI at 25°C. are 1.713 and 1.709 g./cm.³, corresponding to GC contents of 54% and 50%, respectively. Similarly, 5-bromouracil labeled λ DNA halves were separated. The isolation of the four DNA halves made it possible to test for homology in base sequences between the cohesive ends of λ and those of 186. There was no indication of any significant homology in base sequences between the cohesive ends of the two DNA's, as indicated by the absence of a band with intermediate buoyant density in CsCI when either half of 186 DNA was annealed with either half of 5-bromouracil labeled λ DNA and then centrifuged. The lack of cohesion between the two DNA's made it possible to demonstrate unequivocally the formation of interlocked rings (catenanes) between the two DNA's. The existence of a dimeric catenane is evidenced by the formation of a species of intermediate buoyant density when 5-bromouracil labeled λ DNA is cyclized in the presence of cyclic 186 DNA of a relatively high concentration. The molecular weight of one DNA relative to the other can be calculated from the position of the dimeric catenane in a density gradient by using the method of Baldwin. The result was in complete agreement with our previous measurements from the sedimentation coefficients and by electron microscopy. The probability of dimeric catenane formation when one DNA is cyclized in the presence of another DNA is discussed. The experimental results agree with the theoretical expectation.     

Comparative Glucose Catabolism of Xanthomonas Species

Glucose catabolism in eight Xanthomonas species has been comparatively examined by means of the radiorespirometric method. The basic mechanisms for the respective xanthomonads closely resembled each other. The Entner-Doudoroff pathway, in conjunction with the tricarboxylic acid cycle pathway, was the predominant mechanism for glucose catabolism. A small portion (8 to 16%) of substrate glucose was routed into the pentose phosphate pathway. The hexose cycle pathway did not appear to play any significant role in glucose catabolism of these xanthomonads. The results are also consistent with the well-recognized close phylogenic relationship between xanthomonads and pseudomonads.